Status of the World’s Main Report Soil Resources Annex Soil groups, characteristics, distribution and ecosystem services © FAO | Giuseppe Bizzarri © FAO INTERGOVERNMENTAL TECHNICAL PANEL ON SOILS Disclaimer and copyright Recommended citation: FAO and ITPS. 2015. Status of the World’s Soil Resources (SWSR) – Main Report. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils, Rome, Italy The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. 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Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics, | 527 distribution and ecosystem services 1 | Soils with organic layers HISTOSOLS1 In most Histosols organic materials are deposited in a wetland environment to form peat. The waterlogged conditions, oxygen deficiency and, very often in the north, low temperatures, and acidic conditions, inhibit decomposition and lead to accumulation of organic matter (Kolka et al., 2012). In some Histosols the organic material is derived from upland forest vegetation under cool, wet high rainfall conditions. The soil profile features of Histosols reflect the origin of the organic material and the degree of decomposition, while the occurrence of permafrost is a common feature in these soils in arctic landscapes (FAO, 2014; Figure A 1). The soil materials in Histosols are generally dark brown to almost black reflecting the high organic matter content. These soils support forest, sedge and shrubby-moss types of vegetation and occupy a poorly-drained, level topography. However, some Histosols in the coastal areas are found on slopes or form a continuous cover on the terrain, such as blanket bogs. Most of these soils developed during the Holocene Epoch. The age of the basal peat (the peat layer just above the mineral contact) is usually five to nine thousand years old. Histosols are common soils in the Boreal and Arctic landscapes of the Northern hemisphere, although they may also occur in temperate and some tropical regions. Globally, peat lands (organic soils developed on peat) cover approximately 4 million km2 (World Energy Council, 2013). However, most of the Histosols (3.5 million km2) are found in the Northern Circumpolar Permafrost Zone where 76 percent of these soils are perennially frozen (Tarnocai et al., 2009). Nearly 80 percent of all Histosols occur in Russia, Canada and the United States. The global significance of Histosols is that they store huge amounts of organic carbon. It has been estimated that they represent a carbon pool of 500 billion tonnes of organic carbon (Strack, 2008). In addition, the present rate of annual carbon sequestration is approximately 100 million tonnes (Strack, 2008), which exceeds the present carbon loss from these soils due to agriculture, peat extraction and other human-made disturbances. Due to climate change, however, the water-saturated Histosols could be a source of greenhouse gases, mainly in the forms of methane (Couwenberg et al., 2010), but they also could be the source of carbon dioxide if these soils dry out and are affected by wildfires. 1 The Reference Soil Group names of the World Reference Base developed by the IUSS Working Group RB (FAO, 2014) are used. Where the approximate equiv- alent name in the USDA Soil Taxonomy (Soil Survey Staff, 2014) is different, the USDA name is cited in brackets. Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics, | 528 distribution and ecosystem services a Photo by C.Tarnocai b Photo by S. Khokhlov Figure A 1 | (a) A Histosol profile and (b) a peatbog in East-European tundra. Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics, | 529 distribution and ecosystem services 2 | Soils showing a strong human influence ANTHROSOLS (Plagganthrepts, Haplanthrepts, some Orthents) Anthrosols (Figure A 2) are soils formed, altered or influenced by intense human agricultural activities. They are associated with long-term agricultural management in many parts of the world, especially where ancient civilizations were present. Technosols (see below) are also human-influenced but are connected with more recent human activities in industrial and urban environments resulting in the presence of artificial and man- made objects in the soil. The formation of Anthrosols is termed anthropedogenesis. This formation includes various processes induced by human activities in ancient agricultural systems, such as periodic irrigation and drainage, continuous build- up by applying transported manure or other soil materials, and long-term fertilization. These soils are often enriched with phosphorus and carbon, and are characterized by movement and accumulation of clay and clay-organic complexes, reduction and oxidation of iron-manganese oxides and even physical compaction, processes that occur at an accelerated rate compared with that of natural soil changes. This results in a special soil morphology and soil horizon development, such as the formation of a surface horizon with a high organic matter content, the development of compacted plough-pans and the formation of redoximorphic features, all of which represent the outcome of anthropedogenesis. Anthrosols occur widely across the globe. They appear, for example, in ancient agricultural regions under paddy cultivation, or in semi-arid and arid regions where irrigation and sedimentation have occurred. Anthrosols may also show a long-term build-up of elements from long-term manure application and phosphorus enrichment. Globally, the total extent of Anthrosols is estimated at more than 200 million ha, of which 80 percent are cultivated paddy fields. Anthrosols make up the most fertile agricultural land in the world and provide food as an essential ecosystem provisioning service. They often are an inherent part of unique agricultural systems and as such have a cultural function as well. Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics, | 530 distribution and ecosystem services Figure A 2 | (a) An Anthrosol (Plaggen) profile and (b) associated landscape in the Netherlands. a Photo by ISRIC World Soil Information World Photo by ISRIC b Photo by S. Mantel Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics, | 531 distribution and ecosystem services TECHNOSOLS (Non soils) Technosols (Figure A 3) are common soils on all continents. They are dominant in urban areas, where there are only remnants of natural soils and where soils radically transformed by different human activities dominate together with ‘new soils’. The development of particular horizons and layers in such soils is not reflected in natural conditions of the system (Charzyński et al., 2013). Technogenic activities lead to the construction of artificial soil, soil sealing or extraction due to mining of materials not affected by surface processes in natural landscapes. The largest areas of Technosols in comparison to country total area can be found in countries with an extremely high percentage of urbanization such as Belgium and the United Kingdom. The largest areas dominated by Technosols are located within the largest mega-cities, for example the Yangtze River Delta Megalopolis in China (population of about 90 million); the Taiheiyō Belt in Japan, also known as Tokaido corridor (population of nearly 80 million); and the Great Lakes region in the United States (60 million). Technosols are soils of urban, industrial, traffic, mining and military areas. There are four main varieties of